Exploring the time geography of public transport networks with the gtfs2gps package

Journal of Geographical Systems - The creation of the General Transit Feed Specification (GTFS) in the mid-2000s provided a new data format for cities to organize and share digital information on...     

Effect of sub-indicator weighting schemes on the spatial dependence of multidimensional phenomena

Journal of Geographical Systems - The weighting of sub-indicators is widely debated in the composite indicator literature. However, these weighting schemes’ effects on the composite...     

Complex size-dependent habitat associations in potamodromous fish species

Knowledge of the distribution of species life stages at multiple spatial scales is fundamental to both a proper assessment of species management and conservation programmes and the ability to predict the consequences of human disturbances for river systems. The habitat requirements of three native cyprinid species—the Iberian barbel Barbus bocagei Steindachner, the Iberian straight-mouth nase Pseudochondrostoma polylepis (Steindachner), and the Northern straight-mouth nase Pseudochondrostoma duriense (Coelho)—were examined at 174 undisturbed or minimally disturbed sites in 8 river catchments across western Iberia, by modelling occurrence and counts of species life stages at two spatial scales—large (regional) and instream (local)—using hurdle models. All the life stages of the barbel showed a negative association with upstream high-gradient river reaches, whereas juvenile P. duriense favoured such areas. Stream width and openness were negatively related with the occurrence of juvenile and small adult barbel, but not with large adults. Juvenile nase, on the other hand, were found to be mainly confined to fast-flowing habitats with high instream cover and coarser substrata. Advanced life stages of the barbel were mainly associated with the “pure” regional and shared components, whereas the purely local attributes accounted for much of the model variation among nases, in particular juveniles, and juvenile barbel. The results of this study are useful for setting or refining management goals, and highlight the need to separately consider life stages when performing conservation-related studies of species distribution.     

Active surface faulting or landsliding in the Lower Tagus Valley (Portugal)? A solved controversy concerning the Vila Chã de Ourique site

The Lower Tagus Valley has experienced significant (M 6–7) historical seismicity, evidencing the presence of seismogenic faults. These are still deficiently known due to the low strain rates and the recent alluvial sedimentation of the Tagus River that buries most of the structures, though Paleoseismic evidence was allegedly found by a research team in the Tagus valley, at a site 60 km N of Lisbon, near Vila Chã de Ourique (VCO). According to this team, trenching at the VCO site exposed an active thrust fault, evidencing the surface rupture of a large earthquake that occurred in 1531. Our studies performed at this site, comprising field observations with a reappraisal of the trench outcrops previously excavated, borehole drilling, soil mechanics laboratory testing, and seismic reflection acquisition, pointed to the alternative interpretation that the outcropping structures are gravitational and not of tectonic origin. The interpretation of new outcrops crosscutting the structures exposed at the trenches, as well as newly acquired high-resolution seismic reflection data, definitely exclude the active thrust fault explanation and support a gravitational slip model for all the observed structures. Gravitational slip in the river bank slope was promoted by low shear strength clays and high pore water pressure coupled with slope toe river erosion. Gravitational slides must have occurred prior to development of the present sedimentation level of the Tagus alluvial plain, which was attained in the last few thousand years as indicated by borehole data and estimations of sedimentation rates.     

Shaking‐table tests of a full‐scale single‐story masonry veneer wood‐frame structure

This paper presents the findings of shaking‐table experiments conducted to examine the seismic performance of a full‐scale, one‐story, wood‐framed structure with masonry veneer. The structure was designed and constructed in accordance with current U.S. code provisions. The veneer was attached to the wood backing with two kinds of metal anchors, corrugated ties fastened with 8d nails and rigid ties fastened with #8 screws. The tests have shown that the use of nails to fasten veneer anchors to the wood studs is highly unreliable due to the high variation of the nail extraction capacity, which can be influenced by the moisture content of the wood. Other than this, both the wood frame and the masonry veneer performed well under severe ground motions far exceeding a design level earthquake for Seismic Design Category D. Good performance was observed for the rigid veneer ties, which were attached to the wood studs with screws. The results have shown that the veneer walls parallel to the direction of shaking helped to restrain the motion of the wood structure and therefore should not be simply treated as added mass. The detailing of wood roof diaphragms requires special attention in consideration of the out‐of‐plane inertia force of the veneer that can be transmitted through the top plate of the wood‐stud wall to the rim joist. Copyright © 2010 John Wiley & Sons, Ltd.     

The Optical Properties of Greater Florida Bay: Implications for Seagrass Abundance

Water column optical properties of Greater Florida Bay were investigated in the context of their impacts on seagrass distribution. Scattering played an important role in light attenuation throughout the shallow water system. The northwest region was characterized by an absence of seagrasses and the highest scattering by particles, mostly from resuspended carbonate sediments. Higher seagrass densities were observed in the open waters just north of the Florida Keys, where absorption coefficients were dominated by colored dissolved organic material and scattering was lower than in the northwest region. Patchy dense seagrass meadows were observed in the clear waters south of the Keys where scattering and absorption were low and contributed equally to light attenuation. In general, seagrasses were observed in areas where >7.5% of surface irradiance reached the plants and where optical properties were not dominated by scattering. Although the prevention of eutrophication and nuisance algal blooms may be necessary for preserving seagrass meadows in this system, our observations and model calculations indicate that nutrient control alone may be insufficient to permit seagrass recolonization if optical properties are dominated by particulate scattering from resuspended sediments.     

Comparison of sequential extraction and principal component analysis for determination of heavy metal partitioning in sediments: the case of protected Lagoon El Kelbia (Tunisia)

A sequential extraction procedure applied to surface sediments from El Kelbia Lagoon determined the partitioning of Ba, Co, Cr, Cu, Ni, Sr, V and Zn among evaporites, carbonates, Fe–Mn oxides, organic matter and silicates. To validate the procedure, the sequential extraction results (SER) were compared to principal components analysis (PCA) using major and trace element concentrations and mineralogical quantitative data of surface sediments. SER showed that a part of Sr was highly mobile; Cu, Sr, and Zn and a part of Co and Ni were mobile depending on pH conditions; Cr and V were strongly bound to silicate phases; Co and Ni were partitioned between carbonates, oxides and silicates, and a great part of Ba and Sr were bound to organic matter or sulfides. An agreement was found with PCA in terms of partitioning among minerals for most trace elements. Moreover, the absence of correlation between Ca concentrations and the abundances of calcite, gypsum or dolomite could be explained by an important fraction of Ca bound to organic matter. Also, unexpected negative correlations between abundances of smectite and illite could be explained by a transformation of illite into smectite. Thus, SER and PCA were mostly convergent, which enabled: (1) validation of the extraction procedure used, and (2) refinement of interpretations of the origin and relations between minerals.     

Examining the assumptions of integrated coastal management: Stakeholder agendas and elite cooption in Babuyan Islands, Philippines

In the Philippines, Integrated Coastal Management (ICM) represents the dominant response to narratives of ecosystem decline. However, there are persistent challenges to implementation, manifested in continued resource degradation, questioning of the exercise of stakeholder involvement and rising resource conflicts. This paper examines the implementation process and how the assumptions embodied in the ICM regime meet the local reality in one group of islands in the Philippine archipelago. The evidence shows how the transformation towards a supposed equilibrium state of coastal ecosystems is undermined in the face of diverging stakeholder agendas. Expected actors are disempowered by the incoherence between the policy owners’ worldview and reality, paving the way for unethical influence from elite alliances. This is coupled with a deepening of the dominance of state, international development banks, foreign aid agencies, and NGOs in promoting their respective interests. In localities such as the Babuyan Islands, when assumptions of ICM collapse it has destructive consequences for fisherfolk and the coastal environment. We conclude that if ICM is to foster an effective and equitable correction of current unsustainable exploitation patterns, then there is a need to institute improved accountability mechanisms in the devolved governance system as well as taking seriously the espoused commitment to stakeholder involvement in determining the goals and assumptions of ICM.     

Dispersion in Neptune’s zonal wind velocities from NIR Keck AO observations in July 2009

We report observations of Neptune made in H-(1.4–1.8 μm) and K’-(2.0–2.4 μm) bands on 14 and 16 July 2009 from the 10-m W.M. Keck II Telescope using the near-infrared camera NIRC2 coupled to the Adaptive Optics (AO) system. We track the positions of 54 bright atmospheric features over a few hours to derive their zonal and latitudinal velocities, and perform radiative transfer modeling to measure the cloud-top pressures of 50 features seen simultaneously in both bands. We observe one South Polar Feature (SPF) on 14 July and three SPFs on 16 July at ～65?°S. The SPFs observed on both nights are different features, consistent with the high variability of Neptune’s storms. There is significant dispersion in Neptune’s zonal wind velocities about the smooth Voyager wind profile fit of Sromovsky et al. (Icarus, 105:140, 1993), much greater than the upper limit we expect from vertical wind shear, with the largest dispersion seen at equatorial and southern mid-latitudes. Comparison of feature pressures vs. residuals in zonal velocity from the smooth Voyager wind profile also directly reveals the dominance of mechanisms over vertical wind shear in causing dispersion in the zonal winds. Vertical wind shear is not the primary cause of the difference in dispersion and deviation in zonal velocities between features tracked in H-band on 14 July and those tracked in K’-band on 16 July. Dispersion in the zonal velocities of features tracked over these short time periods is dominated by one or more mechanisms, other than vertical wind shear, that can cause changes in the dispersion and deviation in the zonal velocities on timescales of hours to days.